Senator Joseph R. Biden Jr.’s expertise in foreign policy helped raise his standing with Senator Barack Obama, who announced Aug. 24 that Mr. Biden was his choice to be the next vice president of the United States. An Irish Catholic son of Scranton, Pa., the sort of white, working-class city that Mr. Obama is fighting to win this November, Mr. Biden, 66, is in some ways a political elder brother to Mr. Obama: competitive and protective, far more experienced in government and politics, and already a veteran orator when Mr. Obama was still finding his voice.

Mr. Biden has at times acted as blunt-speaking provocateur to Mr. Obama, challenging the younger politician’s ideas and assumptions in ways that Mr. Obama said he wants from his running mate.

A man of strong and many opinions, with a puckish humor and an inability to say no to Sunday news programs, Mr. Biden also has been satirized as the personification of senatorial windiness, though in the presidential debates of this past year he showed new discipline for keeping his comments succinct.

Gov. Sarah Palin, Senator John McCain’s surprising selection on Aug. 29 to be his vice-presidential running mate, took Alaska by surprise, too, not long ago. Though indisputably Alaskan, she rose to prominence by bucking the state's rigid Republican hierarchy, impressing voters more with gumption, warmth and charm than an established record in government.

Before Ms. Palin, 44, became Alaska’s first female governor, in 2006, the top line on her political resume was her tenure as mayor of Wasilla, a growing suburb of Anchorage with fewer than 7,000 residents. Ms. Palin jumped into the governor’s race as an outsider calling for reform, taking on the Republican incumbent. Youthful and sympathetic with voters but bluntly critical of her party’s leadership, she won in a landslide and rolled through the general election.

Now, after barely 20 months in office in a state that has rarely played much of a role in national politics, Ms. Palin is again challenging expectations, including those of her own party.